We plan to investigate peptic fragments of bovine serum albumin (BSA) to learn how such fragments modulate immune responsiveness to the entire BSA molecule. The individual peptides from the enzymatic digest will be isolated and characterized by various biochemical and immunochemical methods. The fragments will be examined for their immunogenic and tolerogenic properties utilizing mice and rabbits as experimental animals. We shall attempt to identify cellular populations which participate in immunomodulation and elucidate their mechanism of action. It is hoped that results of our investigation will provide further insight into the nature of a complex protein antigen. We have chosen to study the immunological properties of the BSA molecule since this protein is well characterized and is being used as an antigen in animal models of immune complex disease.